Objectives of Present Research: Metal matrix composites (MMC) with enhanced material damping can be potential structural materials to improve significantly the stability, control and reliability of space structures. Objectives of this investigation are: - Identify the mechanisms and sources of damping in continuous fiber reinforced MMC (Gr/Al and Gr/Mg) using in situ characterization techniques. - Determine the role of microstructural parameters (fiber volume, fiber orientation, interfiber spacing, grain size, precipitate morphology) in damping. - Define the role of the fiber matrix interface in damping. - Develop high damping structural materials for space applications.